Method and apparatus for forming sand molds

ABSTRACT

A device and method for manufacturing molds for sand casting metallic objects, such as large though thin objects. There is provided a casting pattern disposed between mold means and composed of an elastic and flexible material suction held against a pattern support member operable to shape the mold means in succession as each is cast; said pattern representing a prototype of the metallic object to be cast.

[ Aug. 20, 1974 United States Patent 1 Arbenz et al.

9900 9 2266 2 44 4 66mGM6 11 l 4. -//6 u u t. u

WNW mm l r nmmu a l 3.] o

ZHMSKM 292265 456664 999999 111111 2 77 2 1 1 609987 76638 5 8 6 0v35 67129 064429 380023 [73] Assignee: Schweizeizerische Aluminium AG, v FOREIGN PATENTS 0 APPLICATIONS Chippis, Switzerland May 26, 1970 [21] Appl. No.: 40,487

926,498 4/1947 France............ 962,614 7/1964 Great Britain......................

[22] Filed:

Primary Examiner-Robert D. Baldwin Attorney, Agent, or Firm-Emest F. Marmorek [30] Foreign Application Priority Data May 28, 1969 Switzer1and..............,..........

[51] Int. [58] Field of Search...........

flexible material suction held against a pattern support v 264/225-227, 101; 1 0 member operable to shape the mold means in succes sion as each is cast; said pattern representing a prototype of the metallic object to be cast.

[56] References Cited UNITED STATES PATENTS 25,157 8/1859 Alexander........... 164/235 15 Clams 5 Draw'ng guns lllllllrllll I I METHOD AND APPARATUS FOR FORMING SAN MOLDS BACKGROUND OF THE INVENTION The present invention relates to casting molds and a method of their manufacture especially those for use in sand casting of metallic objects which possess a large surface and a slight thickness, such as panels destined to be used for the covering of facade or front walls.

As far as the covering of face walls are concerned, steadily increasing interest has recently been expressed in such types of metallic sheets, especially those cast of aluminum. On the side which the public views, said metallic sheets frequently display fantasy reliefs, which impart a natural and attractive appearance to that surface. These sheets can possess a more or less profilated cross-section and are usually equipped with eyelets or other fastening devices. As a rule, their surface is relatively large (for example 2 m and more) and their thickness is relatively slight (for example mm or less).

It is known that it is difficult to manufacture sand casting molds for metallic parts with large surface and slight thickness and that difficulties can be encountered in the manufacturing procedures, especially when considerable deviations from a plane surface are involved and, beyond this, when dealing with panels which display the abovementioned fantasy reliefs.

Very frequently it is not possible to use the type of sand or sand mixtures as molding substances which are generally used in aluminum casting plants (green molding sand). If one desires to obtain very large molds with a sufficient degree of mechanical resistance, one will have to resort to using mixtures which are capable of being hardened. The hardening can be brought about through certain admixtures for example, by blowing a gas into the molding substance such as, for example, carbon dioxide, or said hardening process can take place by itself after a more or less long incubation period, for example, when cement is admixed. However, so called mold-masks (CRONING method) can .also be utilized, which had been already hardened through higher temperatures and display a relatively slight thickness. The mold-masks, however, require an expensive model set-up. It is also known that in manufacturing methods, each segment of the mold must be constructed with tapered pattern parts (draft), that is, the surfaces which delineate the mold cavity must be pointed everywhere in such a direction, that the pattern or its parts can be withdrawn from the mold, without the mold being damaged thereby. If there is only an insufficient taper or no taper at all at one section of the mold (the angle between the mold surface in question and the direction of pattern withdrawal), or if the surfaces of the pattern, and consequently those of the mold cavity, are not smooth, one will be forced to divide the pattern into several parts which can be removed individually from the mold, without the latter being damaged thereby. This involves a costly complication with respect to the manufacturing process itself, as well as with respect to subsequent repairs of the mold, said repair jobs being usually necessary in order to remove traces of joints between various pattern parts which are visible on the surface of the mold.

In all customary manufacturing methods for casting molds, the pattern is therefore made of rigid, non- SUMMARY OF THE INVENTION One of the principal objects of the invention is to eliminate the foregoing disadvantages and render feasiblea simple and advantageous manufacture of the aforementioned molds.

Another object of the invention is to eliminate damage to the mold patterns and hence reduce overall costs.

Further objects and advantages of the invention will be set forth in part in the following specification and in part will be obvious therefrom without being specifically referred to, the same being realized and attained as pointed out in the claims hereof.

The invention is characterized that in place of the customary pattern set-up, a pattern is utilized which consists of a flexible material which can be bent in all directions, with said flexible pattern resting on a pattern supporting member.

Such a pattern, which is made of a.bendable, but also elastic material and which generally possesses a large surface anda slight thickness, must come to rest on a pattern supporting member, against the surface of which in a preferred embodiment it tightly clings. The surface of the pattern supporting member corresponds moreover to the shape of the underside of the thin casting piece which is to be subsequently produced.

The surfaces of this pattern are the exact prototype of the surfaces of the desired piece of metal, with all eventual designs and reliefs.

It should be noted, however, that the flexible pattern in different shapes leads only thento the prescribed dimensions of the metallic piece to be cast, when said flexible pattern tightly clings to the shape of the pattern supporting member. During manufacture in accordance with the present invention, the pattern can be bent and deformed due to its flexibility, these deformations being reversible, for example, after withdrawal of the pattern from the mold.

Thus, the pattern must come to lie at each point, as close as possible against the pattern supporting member. In order to achieve this, it is advantageous to create a pressure difference between the two surfaces of the pattern at the time of inserting the latter. This can be achieved, for example, by creating an underpressure (negative or reduced pressure) at the surface of the pattern supporting member against which the pattern will cling.

This may be accomplished in a preferred embodiment by ensuring that the surface of the pattern supporting member which is covered with the pattern, is free-venting; that is, it should be porous or equipped with a network of small holes. These pores and/or holes should open into the interior of the pattern support member and connect with collecting conduits which are arranged there for this purpose and which, in turn,

are connected to an evacuating device. In this manner, the flexible pattern may be positioned quickly and simply against the pattern support member, namely with a precision which is required for the production of the mold. Air cushions between the two surfaces, which touch one another, are thereby avoided.

The free-venting surface of the pattern support member may be comprised of a porous material such as, for example, a combination of wood chips and synthetic resin or of calcined clay and gypsum, also selfhardening and porous concrete.

The shape of this surface corresponds to that of the underside of the metallic sheet to be produced. The pattern, which is the prototype of this sheet, thus can completely adapt itself to this shape.

The material which serves for making the pattern, for example, can be a natural or synthetic, more or less hardened rubber, or can be a synthetic resin which had been treated by a known method in order to impart the necessary flexibility to it. It may also be a composite material such as, for example, a combination of cork and rubber, or any other simple or composite material which has the required characteristics, especially flexibility. In addition, said material must also possess a certain resistance to compression. The demands made of this material, however, are kept within rather narrow limits, especially if molds are produced by a method which is based on a self-hardening combination, which consists of a quick-hardening coating layer and a slower hardening supplementary filling.

Once the pattern is mounted on the pattern support member, the mold is produced in a known manner, namely, from mixtures which are capable of hardening or setting. To give an example, quartz, zicron, or olivine (chrysolite) sand can be utilized together with a polymerizing binding medium, which brings about hardening in less than 1 hour. As far as the hardening process is concerned, one can also make. use of the known action of carbon dioxide with respect to sodium silicate, or employ an analgous newer method, which makes use of the action of an amine (transported in an argon stream) with respect to cyanates and isocyanates, or one can also use silicic acid esters, which bring about the hardening process through hydrolysis, or finally cement or gypsum can be used.

In a preferred embodiment in accordance with the present invention, it is advantageous if those materials are utilized for the production of molds which had been suggested by the applicant in its Swiss Pat. No. 470,220 concerning a method for the production of selfhardening casting molds.

This method consists therein, in that a quick hardening suspension is initially applied onto the surface of the mold, which in a preparatory step had already been coated with an anti-adhesive medium such as paraffin, glycerine, kerosene, etc.

Such suspensions are applied with a brush or are sprayed on in the form of a thin layer and in a short time form a hard compact mask. Prior to the complete hardening of this layer it is advantageous if one applies onto the latter a required quantity of casting sand such as, for example, a mixture of quartz sand. sodium silicate. serving as a binding medium and a suitable hardener so that a compact total unit is formed which displays the desired thickness. Depending on the dimensions of the piece to be cast, this thickness can be in the order of 5 cm or more. One of the following substances can serve as the hardener: sodium fluosilicate, sodium aluminate, bicalcium silicate, sodium zirconium disilicate, etc.

With the above and other objects of the invention in view, the invention consists in the novel methods, construction, arrangement and combination of various devices, elements and parts, as set forth in the claims hereof, one embodiment of the same being illustrated in the accompanying drawings and described in the specification.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description, taken in connection with the accompanying drawings, in which one can follow the different phases of production of a sand casting mold for thin aluminum sheets with rough surfaces for coverings of facade-walls.

BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings, FIG. 1 is a horizontal sectional view of a device for sand casting of metallic objects;

FIG. 2 is a horizontal fragmentary sectional view similar to FIG. 1 but showing the system of FIG. I turned over and the pattern support member withdrawn from the mold;

FIG. 3 is a horizontal sectional view showing the production of the upper mold half with the filling system;

FIG. 4 is a horizontal fragmentary sectional view showing the manner in which the flexible pattern is removed from the two mold halves; and

FIG. 5 is a horizontal sectional view showing the last phase.

DESCRIPTION OF THE PREFERRED EMBODIMENT In carrying the invention into effect in one of the embodiments which has been selected for illustration in the accompanying drawings and for description in this specification, and referring now particularly to FIGS. 1-4, a pattern support member (2) is placed on the workroom floor or onto a stationary or movable mold base (1 As already mentioned, the surface of this pattern support member (2) in a preferred embodiment is penetrable by air (free-venting) and corresponds to the shape of the generally smooth underside of the metal sheet to be cast. Onto the surface of the support member (2), a flexible casting pattern (3) is placed, which then represents an exact prototype of the metal sheet to be cast. In a preferred embodiment it is made of a material which possesses a certain flexibility, said material being rubber, a corresponding synthetic resin, or another material.

In the illustrated preferred embodiment there is shown a prototype which is made of rubber and which, on its upper side, bears a relief corresponding to the one of the metal sheet to be cast.

The flexible pattern (3) can be adapted with perforations (4), should the architectural concept provide for such perforations. These perforations can serve for the accurate placement of gate elements (9) which are to be mounted on the pattern support member (2) and which form a filling system.

In the embodiment shown, conduits (5) are hollowed out in the pattern support member (2), said conduits (5 being connected to an air suction device (for example, a vacuum pump, not shown) for creating an under pressure.

The portions of the pattern support member between the surface on which the flexible pattern (3) should come to lie and the conduits (5), consist of free-venting material having vents or perforations (7). Due to the fact that an under pressure is created in the conduits (5), the flexible pattern (3) under the action of atmospheric air pressure is pulled against the venting surface of the pattern support member (2) and tightly clings thereto. 1

As long as an underpressure is maintained in the pattern support member (2), no danger exists that air pockets will form between the flexible pattern (3) and the pattern support member (2), and the flexible pattern (3) will not shift in the course of the subsequent operations.

Subsequently, a casting box or enclosure (6), which is equipped with customary supplementary means for correct positioning and mounting, is placed on top of the pattern support member (2) by means of guide pins (10). The casting box (6) is filled with a suitable molding material (8), which is capable of hardening and which, in customary manner, is fitted against the rough surface of the flexible pattern (3) which is molded in relief form, so that one ultimately obtains a mold cavity which corresponds to the shape of the flexible pattern (3). As mentioned, any material which is capable of being hardened and which is usable in the production of sand casting molds can be utilized.

When the molding material (8) has reached the desired degree of hardness, the casting box (6), with its contents is turned over. Subsequently, normal atmospheric pressure is re-established in the pattern support member (2), which enables one to separate the hardened mold from the member (2), whereby the flexible pattern (3) remains in position. In other words, the flexible pattern (3) adheres to the surface of the mold half which is located in the casting box (6) and now forms the base portion.

With the aid of the guide pins (10), an upper casting box 11) is set on top of the lower casting box (6). For the filling system, one subsequently affixes the mold segments for the filling funnel and filling ducts (12), together with gates (9). Additional supplementary mold components can be added, such as reinforcing ribs and eyelets for ultimate fastening of the finished product.

Subsequently the upper segment of the mold is produced, namely by filling the upper casting box (11) with a suitable material (8), which can be of the same type as the one used in the lower casting mold (6) or can also have another composition. To give an example, ordinary green casting sand can be used for the upper mold half, or one can use a sand which subsequently can be dried.

When the mold is finished, the upper casting box (11) is lifted off and the supplementary mold components (12), (13) if used, are removed.

The flexible pattern (3) is lifted from the bottom mold half with all necessary care, in order to separate it from the relief-bearing mold surface. The mold segments corresponding to the gates are likewise removed from the bottom mold half.

With the aid of the guiding device (10) the casting boxes (6) and (11) are joined together, so that the newly formed mold cavity (14), which had been created by means of the flexible pattern (3) is closed off.

Subsequently, the metal casting takes place through a filling funnel or other suitable means (12).

lf we are dealing with casting of metallic sheets of relatively simple shape, turningover the casting box (6) (FIG. 2) can be dispensed with. In this case, the operation begins directly with the following step; namely, one in which the above-mentioned casting box (6) is brought into the position which it takes up in accordance with FIG. 2, that is, the casting box (6) is placed on the floor or on another foundation or base (1). The casting box (6) is filled with the suitablemolding material (8) and the mold cavity (14) is formed by pressing the pattern support plate (2) to which, owing to the under pressure, the flexible pattern (3) adheres onto the molding material. In this case and depending on the profile of the mold, a preforming process should be undertaken with the aid of a supplementary tool, forexample with the aid of a template. On the other hand, the casting box (6) will have to be filled partially, that is, up to a level which lies somewhat higher than its surface at the end of the working cycle, so that at all points where the pattern presses against the molding material in order to create the mold cavity (14), a slight consolidation of the molding material (8) takes place. This is necessary in order that the surface of the flexible pat tern (3) is accurately reproduced all over.

We wish it to be understood that we do not desire to be limited to the exact details of construction shown and described, for obvious modifications will occur to a person skilled in the art.

Having thus described the invention, what we claim as new and desire to be secured by Letters Patent, is as follows:

1. A method for the manufacture of hardened molds for sand casting metallic objects, especially those having a large surface and a slight thickness, such as wall panels of aluminum and its alloys,

the improvement comprising:

utilizing a mold pattern composed of an elastic and flexible material and a pattern support plate of a rigid material and creating under pressure between said mold pattern and said pattern support plate while forming a mold half on the other face of said mold pattern.

2. A method, as claimed in claim 1,

further comprising:

placing said pattern on top of said pattern support plate in intimate contact therewith so that it clings thereto whereby at least a portion of a surface of said plate corresponds to the underside shape of a mold to be subsequently cast.

3. A method, as claimed in claim 1,

further comprising:

providing said plate with a surface having vents therein and a conduit system connected therewith whereby an underpressure can be established between said plate and at least a portion of said pattern in contact therewith.

4. A method, as claimed in claim 1,

further comprising:

constructing said pattern of natural or synthetic rubber.

5. A method, as claimed in claim I,

further comprising:

constructing said pattern of synthetic resin.

6. A method, as claimed in claim 1,

further comprising:

constructing said pattern of composite material such as rubber-cork, or rubber-synthetic resin.

7. A method, as claimed in claim 1,

further comprising:

selecting mold materials from substances that harden at different rates of speed.

8. In a method of manufacturing molds for sand casting metallic objects, such as large though thin objects,

the steps comprising:

positioning on a suitable base a pattern support member having conduits;

placing an elastic mold pattern on said support member;

connecting said conduits to suction means;

maintaining an underpressure in said support member with the aid of said conduits and suction means;

placing a first enclosure means on said support member;

filling said first enclosure means with molding material thereby forming a first mold having a shape corresponding to the shape of said mold pattern;

re-establishing normal atmospheric pressure;

disengaging said support member from said first formed mold;

placing a second enclosure means on said first enclosure means;

filling said second enclosure means with molding material thereby forming a second mold having at least a filling channel;

disengaging said first and second enclosure means;

removing said mold pattern from said first formed mold;

joining said first and second enclosure means thereby forming a mold cavity.

9. In a device for manufacturing molds for sand casting metallic objects, especially those having a large surface and a slight thickness, such as panels of aluminum and its alloys,

the improvement comprising:

a mold pattern composed of an elastic and flexible material, a rigid pattern support plate, a face of said pattern support plate conforming to the desired shape of the back surface of the object to be cast, the pattern support plate being permeable to air in the region of its shaped face and containing a system of internal air ducts, and means for applying a vacuum to the ducts so that the mold pattern is positively held in close contact with the whole of the shaped face of the pattern support plate while a mold half is formed on the outer face of the mold pattern.

10. In a device, as claimed in claim 9, wherein said casting pattern is of a synthetic resin.

11. In a device, as claimed in claim 9, wherein said casting pattern is of a composite material selected from the group consisting of rubber-cork and rubbersynthetic resins.

12. In a device, as claimed in claim 9, wherein said casting pattern is of a material selected from the group consisting of natural and synthetic rubbers.

13. In a device, as claimed in claim 9, including a casting box which said mold half is formed within.

14. In a device as claimed in claim 9, wherein said support plate comprises an internal conduit system and a plurality of vents between said conduit system and said shaped surface thereof.

15. In a device as claimed in claim 9, wherein said pattern support plate has a plurality of perforations or pores. 

1. A method for the manufacture of hardened molds for sand casting metallic objects, especially those having a large surface and a slight thickness, such as wall panels of aluminum and its alloys, the improvement comprising: utilizing a mold pattern composed of an elastic and flexible material and a pattern support plate of a rigid material and creating under pressure between said mold pattern and said pattern support plate while forming a mold half on the other Face of said mold pattern.
 2. A method, as claimed in claim 1, further comprising: placing said pattern on top of said pattern support plate in intimate contact therewith so that it clings thereto whereby at least a portion of a surface of said plate corresponds to the underside shape of a mold to be subsequently cast.
 3. A method, as claimed in claim 1, further comprising: providing said plate with a surface having vents therein and a conduit system connected therewith whereby an underpressure can be established between said plate and at least a portion of said pattern in contact therewith.
 4. A method, as claimed in claim 1, further comprising: constructing said pattern of natural or synthetic rubber.
 5. A method, as claimed in claim 1, further comprising: constructing said pattern of synthetic resin.
 6. A method, as claimed in claim 1, further comprising: constructing said pattern of composite material such as rubber-cork, or rubber-synthetic resin.
 7. A method, as claimed in claim 1, further comprising: selecting mold materials from substances that harden at different rates of speed.
 8. In a method of manufacturing molds for sand casting metallic objects, such as large though thin objects, the steps comprising: positioning on a suitable base a pattern support member having conduits; placing an elastic mold pattern on said support member; connecting said conduits to suction means; maintaining an underpressure in said support member with the aid of said conduits and suction means; placing a first enclosure means on said support member; filling said first enclosure means with molding material thereby forming a first mold having a shape corresponding to the shape of said mold pattern; re-establishing normal atmospheric pressure; disengaging said support member from said first formed mold; placing a second enclosure means on said first enclosure means; filling said second enclosure means with molding material thereby forming a second mold having at least a filling channel; disengaging said first and second enclosure means; removing said mold pattern from said first formed mold; joining said first and second enclosure means thereby forming a mold cavity.
 9. In a device for manufacturing molds for sand casting metallic objects, especially those having a large surface and a slight thickness, such as panels of aluminum and its alloys, the improvement comprising: a mold pattern composed of an elastic and flexible material, a rigid pattern support plate, a face of said pattern support plate conforming to the desired shape of the back surface of the object to be cast, the pattern support plate being permeable to air in the region of its shaped face and containing a system of internal air ducts, and means for applying a vacuum to the ducts so that the mold pattern is positively held in close contact with the whole of the shaped face of the pattern support plate while a mold half is formed on the outer face of the mold pattern.
 10. In a device, as claimed in claim 9, wherein said casting pattern is of a synthetic resin.
 11. In a device, as claimed in claim 9, wherein said casting pattern is of a composite material selected from the group consisting of rubber-cork and rubber-synthetic resins.
 12. In a device, as claimed in claim 9, wherein said casting pattern is of a material selected from the group consisting of natural and synthetic rubbers.
 13. In a device, as claimed in claim 9, including a casting box which said mold half is formed within.
 14. In a device as claimed in claim 9, wherein said support plate comprises an internal conduit system and a plurality of vents between said conduit system and said shaped surface thereof.
 15. In a device as claimed in claim 9, wherein said pattern support plate has a plurality of perforations or pores. 